Phosphodiesterase Type 5 Inhibitors: State of the Therapeutic Class

Advancements in Phosphodiesterase 5 Inhibitors: Unveiling Present and Future Perspectives

Phosphodiesterase 5 (PDE5) inhibitors presented themselves as important players in the nitric oxide/cGMP pathway, thus exerting a profound impact on various physiological and pathological processes. Beyond their well-known efficacy in treating male erectile dysfunction (ED) and pulmonary arterial hypertension (PAH), a plethora of studies have unveiled their significance in the treatment of a myriad of other diseases, including cognitive functions, heart failure, multiple drug resistance in cancer therapy, immune diseases, systemic sclerosis and others. This comprehensive review aims to provide an updated assessment of the crucial role played by PDE5 inhibitors (PDE5-Is) as disease-modifying agents taking their limiting side effects into consideration. From a medicinal chemistry and drug discovery perspective, the published PDE5-Is over the last 10 years and their binding characteristics are systemically discussed, and advancement in properties is exposed. A persistent challenge encountered with these agents lies in their limited isozyme selectivity; considering this obstacle, this review also highlights the breakthrough development of the recently reported PDE5 allosteric inhibitors, which exhibit an unparalleled level of selectivity that was rarely achievable by competitive inhibitors. The implications and potential impact of these novel allosteric inhibitors are meticulously explored. Additionally, the concept of multi-targeted ligands is critically evaluated in relation to PDE5-Is by inspecting the broader spectrum of their molecular interactions and effects. The objective of this review is to provide insight into the design of potent, selective PDE5-Is and an overview of their biological function, limitations, challenges, therapeutic potentials, undergoing clinical trials, future prospects and emerging uses, thus guiding upcoming endeavors in both academia and industry within this domain.

Molecular Docking Analysis of Anti-Severe Acute Respiratory Syndrome-Coronavirus 2 Ligands against Spike Glycoprotein and the 3-Chymotrypsin-Like Protease

Background:

The severe acute respiratory syndrome-like disease coronavirus disease 2019 (COVID-19) is a disastrous global pandemic with 16,288,490 infected cases and 649,884 deaths. Until now, no effective treatments are found.

Methods:

The virus uses the 3-chymotrypsin-like protease for inducing the activity of the viral polyproteins and the spike (S) glycoprotein for human cell entry through the human angiotensin-converting enzyme 2 receptor. Blocking the active binding sites of these molecules might be beneficial for decreasing the activity of the virus and suppressing the viral entry to the human cells. Here, docking methods were used to identify a group of ligands may perform the blocking operations.

Results:

The results revealed the strongest binding affinities, sorted high to low, for tadalafil (Cialis) (phosphodiesterase type 5 inhibitor, tirofiban (antiplatelet), paraxanthine (central nervous system stimulant), dexamethasone, gentian violet cation (triphenylmethane), salbutamol, and amlodipine (calcium channel blocker).

Conclusion:

These substances may provide vital help for further clinical investigation in fighting against the current global pandemic of the COVID-19.

Treating male sexual dysfunction after traumatic brain injury: Two case reports

BACKGROUND

Sexual dysfunction is common after traumatic brain injury (TBI) but evaluation of treatment interventions have been sparse.

OBJECTIVE

To report on the treatment of sexual dysfunction for two males with severe TBI.

METHODS AND RESULTS

Case one was treated for erectile dysfunction (ED). After a medical examination which found no underlying physiological problems, Sildenafil was prescribed. Scores on the Golombok Rust Inventory of Sexual Satisfaction Impotence subscale found that scores had improved from the dysfunction range at baseline to the functional range at 6 weeks follow-up. There was some reduction in this improvement at 3 months follow-up, maybe associated with a co-morbid deterioration of emotional state. Case two was treated for idiopathic delayed ejaculation (DE). A standard sex therapy intervention was employed that resulted in the resolution of the problem, documented on the Sex Behavior sub-scale of the Derogatis Inventory for Sexual Functioning-Self Report (comparing baseline to post intervention and follow-up scores).

CONCLUSIONS

The case reports show promise for the treatment of sexual dysfunction after severe TBI using standard medical and sex therapy treatments. In the future, controlled evaluations are required to demonstrate the efficacy of such interventions.

Phosphodiesterase type 5 inhibitors: back and forward from cardiac indications

PDE5 inhibitors (PDE5i) are widely known as treatment for erectile dysfunction (ED). This favorable action has emerged as a "side effect" from pioneering studies when PDE5i have been originally proposed as treatment for coronary artery disease (CAD). PDE5i showed marginal benefits for CAD treatment; although disappointing for that indication, they improved systemic and pulmonary vasodilation and ameliorated general endothelial function. Therefore, PDE5i have been approved and licensed also for pulmonary artery hypertension (PAH), besides ED. Nowadays, fine-tuned biomolecular mechanisms of PDE5i are well recognized to be beneficial onto myocardial contractility and geometry, to reduce tissue fibrosis, hypertrophy and apoptosis. PDE5i consistently exert benefits on heart failure, infarct, cardiomyopathy. The concept that PDE5i likely blunt Th1-driven inflammatory processes, which shift the homeostatic balance from health to disease, has emerged; PDE5i seem to decrease the release of active biomolecules from cells to tissues interested by inflammation. In this view, following clinical and basic research progresses, PDE5i can be undoubtedly "re-allocated" for cardiac indications and, hopefully, they could be approved as therapeutic tools to treat and prevent heart disease. This review aims to summarize PDE5i different clinical applications, from past to present and future, focusing on their potential power as treatment for cardiac diseases.

Structure-Based Design of Novel Tetrahydro-Beta-Carboline Derivatives with a Hydrophilic Side Chain as Potential Phosphodiesterase Inhibitors

Tadalafil is a clinically approved phosphodiesterase-5 inhibitor for the treatment of erectile dysfunction and pulmonary arterial hypertension. It contains two chiral carbons, and the marketed isomer is the 6R, 12aR isomer with a methyl substituent on the terminal nitrogen of the piperazinedione ring. In this report, tadalafil analogues with an extended hydrophilic side chain on the piperazine nitrogen were designed to interact with particular hydrophilic residues in the binding pocket. This leads to analogues with moderate inhibitory activity on phosphodiesterase-5, even for isomers in which chiral carbons are of the S configuration.

A review of analytical methods for the determination of four new phosphodiesterase type 5 inhibitors in biological samples and pharmaceutical preparations

The introduction of oral phosphodiesterase type 5 inhibitor therapy in 1998 revolutionized the treatment of erectile dysfunction. Erectile dysfunction is the most common sexual problem in men. It often has a profound effect on intimate relationships and quality of life. The analysis of pharmaceuticals is an important part of the drug development process as well as for routine analysis and quality control of commercial formulations. Whereas the determination of sildenafil citrate, vardenafil and tadalafil are well documented by a variety of methods, there are few publications about the determination of udenafil, lodenafil carbonate, mirodenafil and avanafil. The paper presents a brief review of the action mechanism, adverse effects, pharmacokinetics and the most recent analytical methods that can determine drug concentration in biological matrices and pharmaceutical formulations of these four drugs.

Erectile dysfunction

Erectile dysfunction is a common clinical entity that affects mainly men older than 40 years. In addition to the classical causes of erectile dysfunction, such as diabetes mellitus and hypertension, several common lifestyle factors, such as obesity, limited or an absence of physical exercise, and lower urinary tract symptoms, have been linked to the development of erectile dysfunction. Substantial steps have been taken in the study of the association between erectile dysfunction and cardiovascular disease. Erectile dysfunction is a strong predictor for coronary artery disease, and cardiovascular assessment of a non-cardiac patient presenting with erectile dysfunction is now recommended. Substantial advances have occurred in the understanding of the pathophysiology of erectile dysfunction that ultimately led to the development of successful oral therapies, namely the phosphodiesterase type 5 inhibitors. However, oral phosphodiesterase type 5 inhibitors have limitations, and present research is thus investigating cutting-edge therapeutic strategies including gene and cell-based technologies with the aim of discovering a cure for erectile dysfunction.

Non-invasive management of primary phosphodiesterase type 5 inhibitor failure in patients with erectile dysfunction

Phosphodiesterase type 5 inhibitors (PDE5-i) have become first line therapy for the treatment of erectile dysfunction. Most initial prescriptions for PDE5-i are by primary care practitioners. Urologists must now routinely manage the patient who has failed initial therapy with PDE5-i. Lifestyle modifications can be of benefit to patients. Patient education and optimization of the PDE5-i can result in a successful response. Interestingly, there are reports of up to 60% salvage after changing the PDE5-i utilized. Daily PDE5-i have shown benefit, and treatment of hypogonadism can enhance response to PDE5-i. We review the management of PDE5-i failures with emphasis on noninvasive approaches to gaining improved erectile response to these medications. An algorithm based on the reviewed strategies is proposed to guide clinicians in the treatment of erectile dysfunction.

Tadalafil in the treatment of erectile dysfunction

The treatment for erectile dysfunction (ED) was revolutionized with the development of phosphodiesterase type 5 (PDE5) inhibitors. Tadalafil (Cialis((R)); Eli Lilly and Company, Indianapolis, IN, USA) is the newest and most versatile PDE5 inhibitor in the clinical armamentarium for the treatment of ED. Its most unique characteristic is its long half-life of 17.5 hours, which lends itself to a longer therapeutic window with on-demand dosing and effective steady-state plasma concentrations with once-daily dosing. Clinical trials have proven its safety and efficacy with both dosing strategies for all severities and etiologies of ED, including difficult-to-treat ED. This thorough review will discuss ED, the physiology of penile erection and the role of PDE5, and all aspects of tadalafil, from its development, through its pharmacology, to its latest clinical studies and indications.

Newer phosphodiesterase inhibitors: comparison with established agents

Erectile dysfunction is defined as the consistent or recurrent inability to attain or maintain penile erection sufficient for sexual performance. Self-reported erectile dysfunction has increased significantly as men seek effective therapy, such as oral phosphodiesterase 5 inhibitors (PDE5i). PDE5i are now the drugs of choice in the initial therapy of erectile dysfunction. This review compares the currently available PDE5i with the second-generation PDE5i, which are soon to be available.

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

The superfamily of cyclic nucleotide (cN) phosphodiesterases (PDEs) is comprised of 11 families of enzymes. PDEs break down cAMP and/or cGMP and are major determinants of cellular cN levels and, consequently, the actions of cN-signaling pathways. PDEs exhibit a range of catalytic efficiencies for breakdown of cAMP and/or cGMP and are regulated by myriad processes including phosphorylation, cN binding to allosteric GAF domains, changes in expression levels, interaction with regulatory or anchoring proteins, and reversible translocation among subcellular compartments. Selective PDE inhibitors are currently in clinical use for treatment of erectile dysfunction, pulmonary hypertension, intermittent claudication, and chronic pulmonary obstructive disease; many new inhibitors are being developed for treatment of these and other maladies. Recently reported x-ray crystallographic structures have defined features that provide for specificity for cAMP or cGMP in PDE catalytic sites or their GAF domains, as well as mechanisms involved in catalysis, oligomerization, autoinhibition, and interactions with inhibitors. In addition, major advances have been made in understanding the physiological impact and the biochemical basis for selective localization and/or recruitment of specific PDE isoenzymes to particular subcellular compartments. The many recent advances in understanding PDE structures, functions, and physiological actions are discussed in this review.

Tadalafil inclusion in microporous silica as effective dissolution enhancer: optimization of loading procedure and molecular state characterization

Tadalafil is an efficient drug used to treat erectile dysfunction characterized by poor water solubility, which has a negative influence on its bioavailability. Utilization of microporous silica represents an effective and facile technology to increase the dissolution rate of poorly soluble drugs. Our strategy involved directly introducing tadalafil as guest molecule into microporous silica as host material by incipient wetness impregnation method. To optimize tadalafil inclusion, response surface methodology (RSM) using 3(3) factorial design was utilized. Furthermore, to investigate the molecular state of tadalafil, Fourier-transform infrared spectroscopy, differential scanning calorimetery, thermal gravimetrical analysis, nitrogen adsorption, and powder X-ray diffraction (PXRD) were carried out. The results obtained pointed out that the quantity of microporous silica was the predominant factor that increased the loading efficiency. For the optimized formula, the loading efficiency was 42.50 wt %. Adsorption-desorption experiments indicated that tadalafil has been introduced into the micropores. Powder XRD and differential scanning calorimetry analyses revealed that tadalafil is arranged in amorphous form. In addition, the dissolution rate of tadalafil from the microporous silica was faster than that of free drug. Amorphous tadalafil occluded in microporous silica did not crystallize over 3 months. These findings contributed in opening a new strategy concerning the utilization of porous silica for the dissolution rate enhancement.

Treatment of erectile dysfunction in the obese type 2 diabetic ZDF rat with adipose tissue-derived stem cells

INTRODUCTION

Erectile dysfunction (ED) is a major complication of type 2 diabetes, and many diabetic men with ED are refractory to common ED therapies.

AIM

To determine whether autologous adipose tissue-derived stem cells (ADSCs) injected into the penis of impotent type 2 diabetic rats improve erectile function.

MAIN OUTCOME MEASURES

Blood glucose levels, intracavernous pressure (ICP) increase upon cavernous nerve (CN) electrostimulation, and immunohistochemistry.

METHODS

Twenty-two male Zucker diabetic fatty (ZDF) rats were used. At 22 weeks of age, all the animals underwent unilateral CN electrostimulation and ICP measurement to confirm impotence. Paragonadal adipose tissue was harvested to procure ADSCs. The impotent animals were randomized to ADSC treatment and sham control groups. At 23 weeks of age, the treatment group animals underwent a penile injection of 1 million ADSCs; the control group animals received vehicle only. Erectile function studies were repeated at 26 weeks of age, followed by tissue harvest.

RESULTS

The rats developed diabetes within the first 10 weeks of age. At 22 weeks of age, 20 out of the 22 rats presented with ED. The post-treatment ICP increase during CN stimulation and ICP increase/mean arterial pressure were significantly higher in the treatment group compared with controls. Three weeks after injection into the corpus cavernosum, only a small number of BrdU-labeled ADSCs was detectable within corporal tissue of the treatment group. There was a significant increase in neuronal nitric oxide synthase (nNOS) in the penile dorsal nerve and in the number of endothelial cells in the corpora cavernosa of the rats in the treatment group.

CONCLUSION

Autologous ADSCs injected into the penis were effective to improve erectile function and to alter the microarchitecture of the corpus cavernosum. Since the number of ADSCs retained in the corpus cavernosum is very small, we postulate that their paracrine function, not trans-differentiation to smooth muscle or endothelial cells, is responsible for the improvement in penile function.

Pharmacogenetics and pharmacogenomics of sexual dysfunction: current status, gaps and potential applications

Although treatment of different types of sexual dysfunction has improved in the past decade with the introduction of phosphodiesterase type 5 inhibitors and selective serotonin reuptake inhibitors, response rates to these targeted therapies are variable. There are a number of studies in the published literature that provide proof-of-concept that genetic variation contributes to the variable response. Pharmacogenomics will most likely be one part of our therapeutic armamentarium in the future and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution. This article will review English language medical literature on the state-of-the-art genetic polymorphisms of drug targets, transporters and signaling molecules as well as pharmacogenetic studies of sexual dysfunction and suggested possible applications. Collectively, the data demonstrate that pharmacogenomics in the field of sexual medicine is still in its infancy. More research will provide further intriguing new discoveries in years to come.